Method, apparatus and computer program

ABSTRACT

An apparatus comprising means for performing: determining an expiration of a service request timer generated in association with a service request message from the apparatus; and handling the expiration of the service request timer based on a determination of a service type of the service request message.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of co-pending U.S. patent applicationSer. No. 17/281,394, filed on Mar. 30, 2021, which is the National Stageof PCT International Application No. PCT/EP2018/077205, filed on Oct. 5,2018. The entire content of the above-referenced applications is herebyincorporated by reference.

TECHNICAL FIELD

Various examples relate to a method, apparatus and a computer program.More particularly, various examples relate to a handling of abnormalcases in a user equipment (UE) in service requests to a 5G network.

BACKGROUND

A communication system can be seen as a facility that enablescommunication sessions between two or more entities such as userterminals, base stations and/or other nodes by providing carriersbetween the various entities involved in the communications path. Acommunication system can be provided for example by means of acommunication network and one or more compatible communication devices.The communication sessions may comprise, for example, communication ofdata for carrying communications such as voice, video, electronic mail(email), text message, multimedia and/or content data and so on.Non-limiting examples of services provided comprise two-way or multi-waycalls, data communication or multimedia services and access to a datanetwork system, such as the Internet.

In a wireless communication system at least a part of a communicationsession between at least two stations occurs over a wireless link.Examples of wireless systems comprise public land mobile networks(PLMN), satellite based communication systems and different wirelesslocal networks, for example wireless local area networks (WLAN). Thewireless systems can typically be divided into cells, and are thereforeoften referred to as cellular systems.

A user can access the communication system by means of an appropriatecommunication device or terminal. A communication device of a user maybe referred to as user equipment (UE) or user device. A communicationdevice is provided with an appropriate signal receiving and transmittingapparatus for enabling communications, for example enabling access to acommunication network or communications directly with other users. Thecommunication device may access a carrier provided by a station, forexample a base station of a cell, and transmit and/or receivecommunications on the carrier.

The communication system and associated devices typically operate inaccordance with a given standard or specification which sets out whatthe various entities associated with the system are permitted to do andhow that should be achieved. Communication protocols and/or parameterswhich shall be used for the connection are also typically defined. Oneexample of a communications system is UTRAN (3G radio). Other examplesof communication systems are the long-term evolution (LTE) of theUniversal Mobile Telecommunications System (UMTS) radio-accesstechnology and so-called 5G or New Radio (NR) networks. NR is beingstandardized by the 3rd Generation Partnership Project (3GPP).

One of the aspects of 5G relates to a Service request procedure. AService request procedure specifies change of the 5GMM (5GS MobilityManagement) mode from IDLE to CONNECTED and the corresponding request toestablish user-plane resources.

In this case the UE is configured to transmit a “SERVICE REQUEST”message to the network side. Standard causes for starting the procedureare, for example, when UE or network have signalling or user datapending and UE is in a 5GMM-IDLE mode. However, this procedure may alsobe invoked when the UE receives a request for emergency servicesfallback (ESFB) from the upper layer and performs ESFB.

Emergency services fallback (ESFB) data sessions may be establishedbetween devices for important communications, for example for calls toan ambulance, police or fire service.

SUMMARY

According to a first aspect, there is provided an apparatus comprisingmeans for: determining an expiration of a service request timergenerated in association with a service request message from theapparatus; and handling the expiration of the service request timerbased on a determination of a service type of the service requestmessage.

The means for handling the expiration of the service request timer basedon a determination of a service type of the service request message maybe further for: initiating at least one emergency service access whenthe service type of the service request message is an emergency servicefallback type; and handing the expiration of the service request timerotherwise.

The means for handling the expiration of the service request timer basedon a determination of a service type of the service request message maybe further for: determining the service type of the service requestmessage is an emergency service fallback type; determining the apparatusis camping on an new radio cell connected to a 5G core network, anemergency services support indicator for access indicates that emergencyservices are supported for evolved universal terrestrial radio accessconnections to the 5G core network only and the apparatus is capable ofaccessing the 5G core network via the evolved universal terrestrialradio access; attempting to select an evolved universal terrestrialradio cell connected to the 5G core network based on the determining;and attempting to select an evolved universal terrestrial radio cellconnected to an evolved packet node when the apparatus is unable toselect an evolved universal terrestrial radio cell connected to the 5Gcore network based on the determining and the apparatus is configured tosupport access via an evolved packet node (S1 mode).

The means for handling the expiration of the service request timer basedon a determination of a service type of the service request message maybe further for: determining the service type of the service requestmessage is an emergency service fallback type; determining the apparatusis camping on an evolved universal terrestrial radio access cellconnected to a 5G core network, an emergency services support indicatorfor access indicates that emergency services are supported for new radioaccess connections to the 5G core network only and the apparatus iscapable of accessing the 5G core network via a new radio access;attempting to select a new radio cell connected to the 5G core networkbased on the determining; and attempting to select an evolved universalterrestrial radio cell connected to an evolved packet node when theapparatus is unable to select a new radio cell connected to the 5G corenetwork based on the determining and the apparatus is configured tosupport access via an evolved packet node (S1 mode).

The means for handling the expiration of the service request timer basedon a determination of a service type of the service request message maybe further for: determining the service type of the service requestmessage is an emergency service fallback type; attempting to select oneof: a new radio cell connected to the 5G core network; an evolveduniversal terrestrial radio cell connected to the 5G core network; andevolved universal terrestrial radio cell connected to an evolved packetnode based on determining the service type of the service requestmessage is an emergency service fallback type and further based on atleast one of: an emergency services support indicator for 3GPP access; aradio access technology of the apparatus current cell (evolved universalterrestrial radio or new radio); a capability to access 5G core networkvia CN via evolved universal terrestrial radio access; support foraccess via an evolved packet node (S1 mode); availability of a suitablenew radio cell connected to the 5G core network, evolved universalterrestrial radio access cell connected to the 5G core network, orevolved universal terrestrial radio access cell connected to an evolvedpacket node; and an emergency service fallback indicator for 3GPPaccess.

The means for handling the expiration of the service request timer basedon a determination of a service type of the service request message maybe further for: performing 5G mobility management specific proceduresand 5G service management procedures to make an emergency packet dataunit session based determining a suitable selection of the new radiocell connected to the 5G core network or the evolved universalterrestrial radio cell connected to the 5G core network; or performingevolved mobility management specific procedures and evolved servicemanagement procedures to make an packet data node connection foremergency bearer services based on determining a suitable selection ofthe evolved universal terrestrial radio cell connected to the evolvedpacket node.

The means for handling the expiration of the service request timer basedon a determination of a service type of the service request message maybe further for handling the expiration of the service request timerbased on a mobility management mode.

The means for handling the expiration of the service request timer basedon a determination of a service type of the service request message anda mobility management mode may be further for: determining the mobilitymanagement mode is an idle mobility management mode and the service typeof the service request message is other than an emergency servicefallback type, and based on the determining: aborting the servicerequest procedure; releasing locally any allocated resources;selectively incrementing a service request counter, wherein the servicerequest counter is not incremented where the service request procedureis configured to establish a packet data unit session for emergencyservices, or the apparatus has an established packet data unit sessionfor emergency services, or the apparatus is configured for high priorityaccess, or the service request was in response to a page or notificationfrom a network; based on the service request counter being equal orgreater a determined threshold value performing: starting a furthertimer, wherein the apparatus is configured not to attempt a furtherservice request until an expiration of the further timer unless at leastone of: the further service request is in response to a page ornotification from a network; the apparatus is configured for highpriority access; the further service request is configured to establisha packet data unit session for emergency services; the apparatus has anestablished packet data unit session for emergency services; theapparatus is registered in a new public land mobile network; andproviding to at least one upper layer a notification that the servicerequest was not accepted where the service request was for a managementobject multimedia telephony voice call.

The means for handling the expiration of the service request timer basedon a determination of a service type of the service request message anda mobility management mode may be further for: determining the mobilitymanagement mode is an connected mobility management mode and the servicetype of the service request message is other than an emergency servicefallback type, and based on the determining: aborting the servicerequest procedure; and setting the apparatus mobility management mode toa connected mode.

The means may be further for: initiating a service request timer with adefined length value, wherein the defined length value is based on thedetermination of the service type of the service request message. Theapparatus may be a user equipment.

According to a second aspect, there is provided an apparatus comprisingat least one processor; and at least one memory including computerprogram; the at least one memory and the computer program codeconfigured to, with the at least one processor, cause the apparatus atleast to perform: determining an expiration of a service request timergenerated in association with a service request message from theapparatus; and handling the expiration of the service request timerbased on a determination of a service type of the service requestmessage.

The apparatus caused to perform handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message may be further caused to perform: initiating at leastone emergency service access when the service type of the servicerequest message is an emergency service fallback type; and handing theexpiration of the service request timer otherwise.

The apparatus caused to perform handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message may be further caused to perform: determining theservice type of the service request message is an emergency servicefallback type; determining the apparatus is camping on an new radio cellconnected to a 5G core network, an emergency services support indicatorfor access indicates that emergency services are supported for evolveduniversal terrestrial radio access connections to the 5G core networkonly and the apparatus is capable of accessing the 5G core network viathe evolved universal terrestrial radio access; attempting to select anevolved universal terrestrial radio cell connected to the 5G corenetwork based on the determining; and attempting to select an evolveduniversal terrestrial radio cell connected to an evolved packet nodewhen the apparatus is unable to select an evolved universal terrestrialradio cell connected to the 5G core network based on the determining andthe apparatus is configured to support access via an evolved packet node(S1 mode).

The apparatus caused to perform handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message may be further caused to perform: determining theservice type of the service request message is an emergency servicefallback type; determining the apparatus is camping on an evolveduniversal terrestrial radio access cell connected to a 5G core network,an emergency services support indicator for access indicates thatemergency services are supported for new radio access connections to the5G core network only and the apparatus is capable of accessing the 5Gcore network via a new radio access; attempting to select a new radiocell connected to the 5G core network based on the determining; andattempting to select an evolved universal terrestrial radio cellconnected to an evolved packet node when the apparatus is unable toselect a new radio cell connected to the 5G core network based on thedetermining and the apparatus is configured to support access via anevolved packet node (S1 mode).

The apparatus caused to perform handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message may be further caused to perform: determining theservice type of the service request message is an emergency servicefallback type; attempting to select one of: a new radio cell connectedto the 5G core network; an evolved universal terrestrial radio cellconnected to the 5G core network; and evolved universal terrestrialradio cell connected to an evolved packet node based on determining theservice type of the service request message is an emergency servicefallback type and further based on at least one of: an emergencyservices support indicator for 3GPP access; a radio access technology ofthe apparatus current cell (evolved universal terrestrial radio or newradio); a capability to access 5G core network via CN via evolveduniversal terrestrial radio access; support for access via an evolvedpacket node (S1 mode); availability of a suitable new radio cellconnected to the 5G core network, evolved universal terrestrial radioaccess cell connected to the 5G core network, or evolved universalterrestrial radio access cell connected to an evolved packet node; andan emergency service fallback indicator for 3GPP access.

The apparatus caused to perform handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message may be further caused to perform: performing 5G mobilitymanagement specific procedures and 5G service management procedures tomake an emergency packet data unit session based determining a suitableselection of the new radio cell connected to the 5G core network or theevolved universal terrestrial radio cell connected to the 5G corenetwork; or performing evolved mobility management specific proceduresand evolved service management procedures to make an packet data nodeconnection for emergency bearer services based on determining a suitableselection of the evolved universal terrestrial radio cell connected tothe evolved packet node.

The apparatus caused to perform handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message may be further caused to perform handling the expirationof the service request timer based on a mobility management mode.

The apparatus caused to perform handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message and a mobility management mode may be further caused toperform: determining the mobility management mode is an idle mobilitymanagement mode and the service type of the service request message isother than an emergency service fallback type, and based on thedetermining: aborting the service request procedure; releasing locallyany allocated resources; selectively incrementing a service requestcounter, wherein the service request counter is not incremented wherethe service request procedure is configured to establish a packet dataunit session for emergency services, or the apparatus has an establishedpacket data unit session for emergency services, or the apparatus isconfigured for high priority access, or the service request was inresponse to a page or notification from a network; based on the servicerequest counter being equal or greater a determined threshold valueperforming: starting a further timer, wherein the apparatus isconfigured not to attempt a further service request until an expirationof the further timer unless at least one of: the further service requestis in response to a page or notification from a network; the apparatusis configured for high priority access; the further service request isconfigured to establish a packet data unit session for emergencyservices; the apparatus has an established packet data unit session foremergency services; the apparatus is registered in a new public landmobile network; and providing to at least one upper layer a notificationthat the service request was not accepted where the service request wasfor a management object multimedia telephony voice call.

The apparatus caused to perform handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message and a mobility management mode may be further caused toperform: determining the mobility management mode is an connectedmobility management mode and the service type of the service requestmessage is other than an emergency service fallback type, and based onthe determining: aborting the service request procedure; and setting theapparatus mobility management mode to a connected mode.

The apparatus may be caused to further perform: initiating a servicerequest timer with a defined length value, wherein the defined lengthvalue is based on the determination of the service type of the servicerequest message.

The apparatus may be a user equipment.

According to a third aspect there is provided an apparatus comprising:service request timer circuitry configured to perform determining anexpiration of a service request timer generated in association with aservice request message from the apparatus; and service request timerexpiration circuitry configured to perform handling the expiration ofthe service request timer based on a determination of a service type ofthe service request message.

According to a fourth aspect there is provided a method comprising:determining an expiration of a service request timer generated inassociation with a service request message from an apparatus; andhandling the expiration of the service request timer based on adetermination of a service type of the service request message.

Handling the expiration of the service request timer based on adetermination of a service type of the service request message mayfurther comprise: initiating at least one emergency service access whenthe service type of the service request message is an emergency servicefallback type; and handing the expiration of the service request timerotherwise.

Handling the expiration of the service request timer based on adetermination of a service type of the service request message mayfurther comprise: determining the service type of the service requestmessage is an emergency service fallback type; determining the apparatusis camping on an new radio cell connected to a 5G core network, anemergency services support indicator for access indicates that emergencyservices are supported for evolved universal terrestrial radio accessconnections to the 5G core network only and the apparatus is capable ofaccessing the 5G core network via the evolved universal terrestrialradio access; attempting to select an evolved universal terrestrialradio cell connected to the 5G core network based on the determining;and attempting to select an evolved universal terrestrial radio cellconnected to an evolved packet node when the apparatus is unable toselect an evolved universal terrestrial radio cell connected to the 5Gcore network based on the determining and the apparatus is configured tosupport access via an evolved packet node (S1 mode).

Handling the expiration of the service request timer based on adetermination of a service type of the service request message mayfurther comprise: determining the service type of the service requestmessage is an emergency service fallback type; determining the apparatusis camping on an evolved universal terrestrial radio access cellconnected to a 5G core network, an emergency services support indicatorfor access indicates that emergency services are supported for new radioaccess connections to the 5G core network only and the apparatus iscapable of accessing the 5G core network via a new radio access;attempting to select a new radio cell connected to the 5G core networkbased on the determining; and attempting to select an evolved universalterrestrial radio cell connected to an evolved packet node when theapparatus is unable to select a new radio cell connected to the 5G corenetwork based on the determining and the apparatus is configured tosupport access via an evolved packet node (S1 mode).

Handling the expiration of the service request timer based on adetermination of a service type of the service request message mayfurther comprise: determining the service type of the service requestmessage is an emergency service fallback type; attempting to select oneof: a new radio cell connected to the 5G core network; an evolveduniversal terrestrial radio cell connected to the 5G core network; andevolved universal terrestrial radio cell connected to an evolved packetnode based on determining the service type of the service requestmessage is an emergency service fallback type and further based on atleast one of: an emergency services support indicator for 3GPP access; aradio access technology of the apparatus current cell (evolved universalterrestrial radio or new radio); a capability to access 5G core networkvia CN via evolved universal terrestrial radio access; support foraccess via an evolved packet node (S1 mode); availability of a suitablenew radio cell connected to the 5G core network, evolved universalterrestrial radio access cell connected to the 5G core network, orevolved universal terrestrial radio access cell connected to an evolvedpacket node; and an emergency service fallback indicator for 3GPPaccess.

Handling the expiration of the service request timer based on adetermination of a service type of the service request message mayfurther comprise: performing 5G mobility management specific proceduresand 5G service management procedures to make an emergency packet dataunit session based determining a suitable selection of the new radiocell connected to the 5G core network or the evolved universalterrestrial radio cell connected to the 5G core network; or performingevolved mobility management specific procedures and evolved servicemanagement procedures to make an packet data node connection foremergency bearer services based on determining a suitable selection ofthe evolved universal terrestrial radio cell connected to the evolvedpacket node.

Handling the expiration of the service request timer based on adetermination of a service type of the service request message mayfurther comprise handling the expiration of the service request timerbased on a mobility management mode.

Handling the expiration of the service request timer based on adetermination of a service type of the service request message and amobility management mode may further comprise: determining the mobilitymanagement mode is an idle mobility management mode and the service typeof the service request message is other than an emergency servicefallback type, and based on the determining: aborting the servicerequest procedure; releasing locally any allocated resources;selectively incrementing a service request counter, wherein the servicerequest counter is not incremented where the service request procedureis configured to establish a packet data unit session for emergencyservices, or the apparatus has an established packet data unit sessionfor emergency services, or the apparatus is configured for high priorityaccess, or the service request was in response to a page or notificationfrom a network; based on the service request counter being equal orgreater a determined threshold value performing: starting a furthertimer, wherein the apparatus is configured not to attempt a furtherservice request until an expiration of the further timer unless at leastone of: the further service request is in response to a page ornotification from a network; the apparatus is configured for highpriority access; the further service request is configured to establisha packet data unit session for emergency services; the apparatus has anestablished packet data unit session for emergency services; theapparatus is registered in a new public land mobile network; andproviding to at least one upper layer a notification that the servicerequest was not accepted where the service request was for a managementobject multimedia telephony voice call.

Handling the expiration of the service request timer based on adetermination of a service type of the service request message and amobility management mode may further comprise: determining the mobilitymanagement mode is an connected mobility management mode and the servicetype of the service request message is other than an emergency servicefallback type, and based on the determining: aborting the servicerequest procedure; and setting the apparatus mobility management mode toa connected mode.

The method may further comprise: initiating a service request timer witha defined length value, wherein the defined length value is based on thedetermination of the service type of the service request message.

According to an fifth aspect there is provided a computer programcomprising instructions for causing an apparatus to perform at least thefollowing: determining an expiration of a service request timergenerated in association with a service request message from theapparatus; and handling the expiration of the service request timerbased on a determination of a service type of the service requestmessage.

According to a sixth aspect there is provided a non-transitory computerreadable medium comprising program instructions for causing an apparatusto perform at least the following: determining an expiration of aservice request timer generated in association with a service requestmessage from the apparatus; and handling the expiration of the servicerequest timer based on a determination of a service type of the servicerequest message.

According to a seventh aspect, there is provided a computer programcomprising instructions for causing an apparatus to perform at least thefollowing: determining an expiration of a service request timergenerated in association with a service request message from theapparatus; and handling the expiration of the service request timerbased on a determination of a service type of the service requestmessage.

In the above, various aspects have been described. It should beappreciated that further aspects may be provided by the combination ofany two or more of the aspects described above.

Various other aspects and further embodiments are also described in thefollowing detailed description and in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist understanding of the present disclosure and to show how someembodiments may be put into effect, reference is made by way of exampleonly to the accompanying drawings in which:

FIG. 1 shows schematically an example of a system within which someembodiments may be employed;

FIG. 2 shows schematically an example of a message flow for requesting aservice request and handling a timer expiration according to someembodiments;

FIG. 3 shows schematically a flow diagram of handling a timer expirationbased on 5GMM mode and service type according to some embodiments;

FIG. 4 shows schematically a first part, idle-non emergency servicesfall-back based, handling a timer expiration based on 5GMM mode andservice type according to some embodiments as shown in FIG. 3 ;

FIG. 5 shows schematically a second part, connected-non emergencyservices fall-back based, handling a timer expiration based on 5GMM modeand service type according to some embodiments as shown in FIG. 3 ;

FIG. 6 shows schematically a third, emergency services fall-back based,handling a timer expiration according to some embodiments as shown inFIG. 3 ;

FIG. 7 shows schematically a further third, emergency services fall-backbased, handling a timer expiration according to some embodiments asshown in FIG. 3 ; and

FIG. 8 shows schematically an example of an apparatus suitable forimplementing the handling of the timer expiration according to someembodiments.

DETAILED DESCRIPTION

Some examples may be provided in the context of emergency data sessions.

As discussed above the process by which the UE is configured to transmita “SERVICE REQUEST” message to the network side and the handling ofabnormal cases is one of current discussion.

One “abnormal case” is when a service request timer, defined as T3517 insome discussions expires. The T3517 timer is started whenever the“SERVICE REQUEST” message is sent by the UE, and (normally) stopped whena response from the network is received.

For the case that T3517 expires (in other words the UE does not receivea response from the network) there are defined procedures that the UEmay follow. However, until now these procedures are defined only forcases when the service request procedure was invoked by “normal” causes(i.e. pending signalling/data), and not for the case when the servicerequest procedure was invoked because of emergency service fallback(ESFB).

The concept as discussed in further detail hereafter is the provision ofsuitable timer (T3517) expiration handling (in other words in case theUE does not receive a response from the network) which takes intoconsideration when the service request procedure has been invoked byemergency services fall back requirements. As discussed in detailhereafter apparatus such as a user equipment implementing suchembodiments can handle and prevent failure of an emergency session whichcould be caused by such timer expiration.

The embodiments as discusses herein describes mechanisms for handlingthe specific case when a service request procedure is invoked by anemergency service fallback (ESFB) and where the timer (T3517) expiresand discloses different ways of trying to establish an emergencysession. For example to select a new radio (NR) cell connected to 5Gcore network (5GCN), then an evolved UTRA (E-UTRA) cell connected to5GCN, then an E-UTRA cell connected to an evolved packet core (EPC).

In a wireless communication system 100, such as that shown in FIG. 1 ,mobile communication devices or user equipment (UE) 102, 104, 105 areprovided wireless access via at least one base station or similarwireless transmitting and/or receiving node or point. Base stations aretypically controlled by at least one appropriate controller apparatus,so as to enable operation thereof and management of mobile communicationdevices in communication with the base stations. The controllerapparatus may be located in a radio access network (e.g. wirelesscommunication system 100) or in a core network (CN) (not shown) and maybe implemented as one central apparatus or its functionality may bedistributed over several apparatuses. The controller apparatus may bepart of the base station and/or provided by a separate entity such as aRadio Network Controller. In FIG. 1 control apparatus 108 and 109 areshown to control the respective macro level base stations 106 and 107.The control apparatus of a base station can be interconnected with othercontrol entities. The control apparatus is typically provided withmemory capacity and at least one data processor. The control apparatusand functions may be distributed between a plurality of control units.In some systems, the control apparatus may additionally or alternativelybe provided in a radio network controller.

In FIG. 1 base stations 106 and 107 are shown as connected to a widercommunications network 113 via gateway 112. A further gateway functionmay be provided to connect to another network.

The smaller base stations 116, 118 and 120 may also be connected to thenetwork 113, for example by a separate gateway function and/or via thecontrollers of the macro level stations. The base stations 116, 118 and120 may be pico or femto level base stations or the like. In theexample, stations 116 and 118 are connected via a gateway 111 whilststation 120 connects via the controller apparatus 108. In someembodiments, the smaller stations may not be provided. Smaller basestations 116, 118 and 120 may be part of a second network, for exampleWLAN and may be WLAN APs.

The communication devices 102, 104, 105 may access the communicationsystem based on various access techniques, such as code divisionmultiple access (CDMA), or wideband CDMA (WCDMA). Other non-limitingexamples comprise time division multiple access (TDMA), frequencydivision multiple access (FDMA) and various schemes thereof such as theinterleaved frequency division multiple access (IFDMA), single carrierfrequency division multiple access (SC-FDMA) and orthogonal frequencydivision multiple access (OFDMA), space division multiple access (SDMA)and so on.

An example of wireless communication systems are architecturesstandardized by the 3rd Generation Partnership Project (3GPP). A latest3GPP based development is often referred to as the long term evolution(LTE) of the Universal Mobile Telecommunications System (UMTS)radio-access technology. The various development stages of the 3GPPspecifications are referred to as releases. More recent developments ofthe LTE are often referred to as LTE Advanced (LTE-A). The LTE (LTE-A)employs a radio mobile architecture known as the Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) and a core network known asthe Evolved Packet Core (EPC). Base stations of such systems are knownas evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features suchas user plane Packet Data Convergence/Radio Link Control/Medium AccessControl/Physical layer protocol (PDCP/RLC/MAC/PHY) and control planeRadio Resource Control (RRC) protocol terminations towards thecommunication devices. Other examples of radio access system comprisethose provided by base stations of systems that are based ontechnologies such as wireless local area network (WLAN) and/or WiMax(Worldwide Interoperability for Microwave Access). A base station canprovide coverage for an entire cell or similar radio service area. Corenetwork elements include Mobility Management Entity (MME), ServingGateway (S-GW) and Packet Gateway (P-GW).

An example of a suitable communications system is the 5G or NR concept.Network architecture in NR may be similar to that of LTE-advanced. Basestations of NR systems may be known as next generation Node Bs (gNBs).Changes to the network architecture may depend on the need to supportvarious radio technologies and finer QoS support, and some on-demandrequirements for e.g. QoS levels to support QoE of user point of view.Also network aware services and applications, and service andapplication aware networks may bring changes to the architecture. Thoseare related to Information Centric Network (ICN) and User-CentricContent Delivery Network (UC-CDN) approaches. NR may use multipleinput-multiple output (MIMO) antennas, many more base stations or nodesthan the LTE (a so-called small cell concept), including macro sitesoperating in co-operation with smaller stations and perhaps alsoemploying a variety of radio technologies for better coverage andenhanced data rates.

Future networks may utilise network functions virtualization (NFV) whichis a network architecture concept that proposes virtualizing networknode functions into “building blocks” or entities that may beoperationally connected or linked together to provide services. Avirtualized network function (VNF) may comprise one or more virtualmachines running computer program codes using standard or general typeservers instead of customized hardware. Cloud computing or data storagemay also be utilized. In radio communications this may mean nodeoperations to be carried out, at least partly, in a server, host or nodeoperationally coupled to a remote radio head. It is also possible thatnode operations will be distributed among a plurality of servers, nodesor hosts. It should also be understood that the distribution of labourbetween core network operations and base station operations may differfrom that of the LTE or even be non-existent.

An example 5G core network (CN) comprises functional entities. The CN isconnected to a UE via the radio access network (RAN). An UPF (User PlaneFunction) whose role is called PSA (PDU Session Anchor) may beresponsible for forwarding frames back and forth between the DN (datanetwork) and the tunnels established over the 5G towards the UE(s)exchanging traffic with the DN.

The UPF is controlled by an SMF (Session Management Function) thatreceives policies from a PCF (Policy Control Function). The CN may alsoinclude an AMF (Access & Mobility Function).

FIG. 2 shows an overview of deployed embodiments. In FIG. 2 , an UE 202is configured to start a request timer (also defined as T3517 in thefollowing disclosure). This is shown in FIG. 2 by step 201. The value ofthe request timer (T3517) may differ based on the reason fortransmitting a service request. For example, the default value of T3517can be 10 seconds if a service request is sent due to emergency servicefallback and otherwise, the default value of T3517 can be 15 seconds.

The UE 202 may furthermore be configured to generate and transmit aservice request to the access and mobility function (AMF) 204 as shownin step 203.

After a defined time the timer (T3517) expires as shown in FIG. 2 bystep 205.

The user equipment 202 is then configured to determine the current 5Gmobility management mode (5GMM mode) and also the service request typeas shown in FIG. 207 . This determination may be explicit in that the UEperforms a explicit determination of these parameters or may be implicitin that there is stored within the UE the parameter values which may beretrieved.

The user equipment 202 may then be configured to handle the timer(T3517) expiration based on the service type and furthermore the 5GMMmode (values) as shown in FIG. 2 by step 209.

FIG. 3 shows furthermore the handling of the timer (T3517) expirationbased on the service type and furthermore the 5GMM mode (values) asshown in FIG. 2 by step 209 in further detail and according to someembodiments.

In some embodiments the handling of the timer expiration causes the UEto enter the state 5GMM-Registered as shown in FIG. 3 by step 301.

Then the UE is configured in some embodiments to perform a 5GMM mode andservice type check as shown in FIG. 3 by step 303.

Where the 5GMM mode and service type check determines that the 5GMM modeis a 5GMM-Idle mode and that the service request type is not emergencyservice fallback then the user equipment may be configured to implementIdle-Non ESFB handling as shown in FIG. 3 by step 305.

Where the 5GMM mode and service type check determines that the 5GMM modeis a 5GMM-connected mode and that the service request type is notemergency service fallback then the user equipment may be configured toimplement Connected-Non ESFB handling as shown in FIG. 3 by step 307.

Where the 5GMM mode and service type check determines that the servicerequest type is emergency service fallback then the user equipment maybe configured to implement ESFB handling as shown in FIG. 3 by step 309.

With respect to FIG. 4 the is shown in further detail proceduresassociated with the Idle-Non ESFB handling as shown in FIG. 3 by step305.

The user equipment in some embodiments in implementing Idle-Non ESFBhandling is configured to increment a service request counter, to abortthe procedure and release locally any allocated resources.

If the UE triggered the service request procedure in 5GMM-IDLE mode andthe service type of the SERVICE REQUEST message was not set to“emergency services fallback”, then the 5GMM sublayer shall incrementthe service request attempt counter subject the exclusions noted below,abort the procedure and release locally any resources allocated for theservice request procedure as shown in FIG. 4 by step 401.

In some embodiments the service request attempt counter is notincremented where the service request procedure is initiated toestablish a PDU session for emergency services or the UE has a PDUsession for emergency services established or the UE is a UE configuredfor high priority access in selected PLMN or the service request isinitiated in response to paging or notification from the network.

In some embodiments the UE is then configured to check whether theservice request attempt counter is greater than or equal to 5 as shownin FIG. 4 by step 403.

When the service request attempt counter is greater than or equal to 5,the UE is configured to start a further timer (this timer may be definedas timer T3525 in the following disclosure) as shown in FIG. 4 by step405.

Furthermore in some embodiments the UE is configured to determinewhether the service request was initiated for a management object (MO)multimedia telephony (MMTEL) voice call as shown in FIG. 4 by step 407.Where the service request was a MO MMTEL voice call then the UE isconfigured to generate a notification that the service request was notaccepted due to the UE having started the further timer (T3525) isprovided to the upper layers as shown in FIG. 4 by step 409. In someembodiments this can result in the upper layers requestingimplementation specific mechanisms, for example the MMTEL voice callbeing attempted to another internet property connectivity access network(IP-CAN), or establishment of a circuit switched (CS) voice call (ifsupported and not already attempted in the CS domain).

In some embodiments the UE is configured to not attempt a servicerequest until expiry of the further timer (T3525) unless one of thefollowing conditions are met:

1) the service request is initiated in response to paging ornotification from the network;

2) the UE is a UE configured for high priority access in selected PLMN;

3) the service request is initiated to establish a protocol data unit(PDU) session for emergency services;

4) the UE has a PDU session for emergency services established; or

5) the UE is registered in a new public land mobile network (PLMN).

In some embodiments the non-access stratum (NAS) signalling connectioncan also be released if the UE deems that the network has failed anauthentication check.

With respect to FIG. 5 the is shown in further detail proceduresassociated with the Connected-Non ESFB handling as shown in FIG. 3 bystep 307.

The user equipment in some embodiments in implementing Connected-NonESFB handling is configured to abort a 5GMM Sublayer procedure as shownin FIG. 5 by step 501.

The user equipment in some embodiments is further configured to staywithin the 5GMM-connected mode as shown in FIG. 5 by step 503.

With respect to FIG. 6 the is shown in further detail a first set ofexample procedures associated with the ESFB handling as shown in FIG. 3by step 309.

The user equipment in some embodiments in implementing Connected-NonESFB handling is configured to determine which type of cell the UE iscamping on when connected to the 5G Core Network as shown in FIG. 6 bystep 601.

Where the UE is camping on an NR cell connected to 5GCN then the UE isconfigured to determine whether an emergency services support indicatorfor 3GPP access indicates “emergency services supported in E-UTRAconnected to 5GCN only” or option (1). Otherwise the UE may beconfigured to determine whether an emergency services support indicatorfor 3GPP access indicates “emergency services not supported” or UE isnot capable of accessing 5GCN via E-UTRA or option (2). Thedeterminations may be shown in FIG. 6 by step 603.

Where the determination is option (1) emergency services supportindicator for 3GPP access indicates “emergency services supported inE-UTRA connected to 5GCN only” then the UE is configured to determinewhether it is capable of accessing 5GCN via E-UTRA and if so then the UEis further configured to attempt to select an E-UTRA cell connected to5GCN.

If the UE does not find a suitable E-UTRA cell connected to 5GCN and theUE supports S1 mode, then the UE is configured to attempt to select anE-UTRA cell connected to the evolved packet core (EPC).

These operations are shown in FIG. 6 by step 605.

Where the determination is option (2), where the emergency servicessupport indicator for 3GPP access indicates “emergency services notsupported” or the UE is not capable of accessing 5GCN via E-UTRA and ifthe UE supports S1 mode, the UE shall attempt to select an E-UTRA cellconnected to EPC as shown in FIG. 6 by step 607. Here, even if theemergency services support indicator for 3GPP access indicates“emergency services not supported”, the UE may choose to attempt toselect an E-UTRA cell connected to 5GCN if the UE is capable ofaccessing 5GCN via E-UTRA and the emergency service fallback indicatorfor 3GPP access indicates “Emergency services fallback supported in NRconnected to 5GCN and E-UTRA connected to 5GCN” in order to perform ESFBin an E-UTRA cell connected to 5GCN. In this case, if the UE does notfind a suitable E-UTRA cell connected to 5GCN and the UE supports S1mode, then the UE is configured to attempt to select an E-UTRA cellconnected to the EPC.

Where the UE is camping on an E-UTRA cell connected to 5GCN then the UEis configured to determine whether an emergency services supportindicator for 3GPP access indicates “emergency services supported inE-UTRA connected to NR only” or option (3). Otherwise the UE may beconfigured to determine whether an emergency services support indicatorfor 3GPP access indicates “emergency services not supported” or UE isnot capable of accessing 5GCN via NR or option (4). The determinationsmay be shown in FIG. 6 by step 604.

Where the determination is option (3) emergency services supportindicator for 3GPP access indicates “emergency services supported in NRconnected to 5GCN only” then the UE is configured to determine whetherit is capable of accessing 5GCN via NR and if so then the UE is furtherconfigured to attempt to select an NR cell connected to 5GCN.

If the UE does not find a suitable NR cell connected to 5GCN and the UEsupports S1 mode, then the UE is configured to attempt to select anE-UTRA cell connected to the evolved packet core (EPC).

These operations are shown in FIG. 6 by step 606.

Where the determination is option (4), where the emergency servicessupport indicator for 3GPP access indicates “emergency services notsupported” or the UE is not capable of accessing 5GCN via NR and if theUE supports S1 mode, the UE shall attempt to select an E-UTRA cellconnected to EPC as shown in FIG. 6 by step 607. Here, even if theemergency services support indicator for 3GPP access indicates“emergency services not supported”, the UE may choose to attempt toselect an NR cell connected to 5GCN if the UE is capable of accessing5GCN via NR and the emergency service fallback indicator for 3GPP accessindicates “Emergency services fallback supported in NR connected to 5GCNand E-UTRA connected to 5GCN” in order to perform ESFB in an NR cellconnected to 5GCN. In this case, if the UE does not find a suitable NRcell connected to 5GCN and the UE supports S1 mode, then the UE isconfigured to attempt to select an E-UTRA cell connected to the EPC.

If the UE finds a suitable NR cell connected to 5GCN, E-UTRA cellconnected to 5GCN or E-UTRA cell connected to EPC the UE is thenconfigured to:

proceed with appropriate 5GMM specific procedures and 5GSM procedures tomake an emergency PDU session; or

proceed with appropriate EPS mobility management (EMM) specificprocedures and, if necessary, EPS session management (ESM) procedures tomake a packet data network (PDN) connection for emergency bearerservices.

The proceeding with appropriate 5GMM or EMM/ESM procedures is shown inFIG. 6 by step 608.

With respect to FIG. 7 is shown a further set of example proceduresassociated with the ESFB handling as shown in FIG. 3 by step 309.

The user equipment in some embodiments in implementing Connected-NonESFB handling is configured to select an NR cell connected to 5GCN,E-UTRA cell connected to 5GCN, or an E-UTRA cell connected to EPC basedon at least one of the followings:

1) the emergency services support indicator for 3GPP access;

2) the radio access technology of the current cell (either E-UTRA orNR);

3) the UE's capability to access 5GCN via E-UTRA;

4) the UE's support for S1 mode;

5) availability of a suitable NR cell connected to 5GCN, E-UTRA cellconnected to 5GCN or E-UTRA cell connected to EPC; and

6) the emergency service fallback indicator for 3GPP access.

The selection of NR cell connected to 5GCN, E-UTRA cell connected to5GCN, or an E-UTRA cell connected to EPC is shown in FIG. 7 by step 701.

If the UE finds a suitable NR cell connected to 5GCN, E-UTRA cellconnected to 5GCN or E-UTRA cell connected to EPC the UE is thenconfigured to:

proceed with appropriate 5GMM specific procedures and 5GSM procedures tomake an emergency PDU session; or

proceed with appropriate EPS mobility management (EMM) specificprocedures and, if necessary, EPS session management (ESM) procedures tomake a packet data network (PDN) connection for emergency bearerservices.

The proceeding with appropriate 5GMM or EMM/ESM procedures is shown inFIG. 7 by step 608.

In some embodiments the UE may be further configured to control otheraspects based on the abnormal event determination.

FIG. 8 shows an example apparatus 850 in which embodiments of theinvention may be applied. Apparatus 850 may be an element of the systemshown in FIG. 1 . In some example embodiments, the apparatus 850 may, beembodied as, or included as a component of, a communications device withwired or wireless communications capabilities. The example apparatus mayinclude or otherwise be in communication with one or more processors852, memory devices 854, Input/Output (I/O) interfaces 856,communications interfaces 858 and/or user interfaces 860 (in FIG. 8 ,one of each is shown as an example). Depending on the component of FIG.1 being implemented by the apparatus, however, the apparatus may includeadditional elements and/or may not include one or more of the foregoingelements, such as the user interfaces.

Apparatus 850 may be a user equipment.

The processor 852 may be embodied as various means for implementing thevarious functionalities of example embodiments of the present inventionincluding, for example, one or more of a microprocessor, a coprocessor,a controller, a special-purpose integrated circuit such as, for example,an ASIC (application specific integrated circuit), an FPGA (fieldprogrammable gate array), DSP (digital signal processor), or a hardwareaccelerator, processing circuitry or other similar hardware. Accordingto one example embodiment, the processor may be representative of aplurality of processors, or one or more multi-core processors, operatingindividually or in concert.

Whether configured as hardware alone or via instructions stored on acomputer-readable storage medium, or by a combination thereof, theprocessor 652 may be an apparatus configured to perform operationsaccording to embodiments of the present invention while configuredaccordingly. Thus, in example embodiments where the processor isembodied as, or is part of, an ASIC, FPGA, or the like, the processor isspecifically configured hardware for conducting the operations describedherein.

Alternatively, in examples where the processor is an executor ofinstructions stored on a computer-readable storage medium, theinstructions specifically configure the processor to perform thealgorithms and operations described herein. In some example embodiments,the processor is a processor of a specific device configured foremploying example embodiments of the present invention by furtherconfiguration of the processor via executed instructions for performingthe algorithms, methods, and operations described herein.

The memory device 854 may be one or more computer-readable storage mediathat may include volatile and/or non-volatile memory. In some exampleembodiments, the memory device may include Random Access Memory (RAM)including dynamic and/or static RAM, on-chip or off-chip cache memory,and/or the like. Further, the memory device may include non-volatilememory, which may be embedded and/or removable, and may include, forexample, Read-Only Memory (ROM), flash memory, magnetic storage devices(for example, hard disks, floppy disk drives, magnetic tape, etc.),optical disc drives and/or media, non-volatile random access memory(NVRAM), and/or the like. The memory device may include a cache area fortemporary storage of data. In this regard, at least a portion or theentire memory device may be included within the processor 852.

Further, the memory device 854 may be configured to store information,data, applications, computer-readable program code instructions, and/orthe like for enabling the processor 852 and the example apparatus 850 tocarry out various functions in accordance with example embodiments ofthe present invention described herein. For example, the memory devicemay be configured to buffer input data for processing by the processor.Additionally, or alternatively, the memory device may be configured tostore instructions for execution by the processor. The memory may besecurely protected, with the integrity of the data stored therein beingensured. In this regard, data access may be checked with authenticationand authorized based on access control policies.

The I/O interface 856 may be any device, circuitry, or means embodied inhardware, software or a combination of hardware and software that isconfigured to interface the processor 852 with other circuitry ordevices, such as the communications interface 858 and/or the userinterface 860. In some example embodiments, the processor may interfacewith the memory device via the I/O interface. The I/O interface may beconfigured to convert signals and data into a form that may beinterpreted by the processor. The I/O interface may also performbuffering of inputs and outputs to support the operation of theprocessor. According to some example embodiments, the processor and theI/O interface may be combined onto a single chip or integrated circuitconfigured to perform, or cause the apparatus 202 to perform, variousfunctionalities of an example embodiment.

The communication interface 858 may be any device or means embodied inhardware, software or a combination of hardware and software that isconfigured to receive and/or transmit data from/to one or more networks864 and/or any other device or module in communication with the exampleapparatus 850. The processor may also be configured to facilitatecommunications via the communications interface by, for example,controlling hardware included within the communications interface. Inthis regard, the communication interface may include, for example, oneor more antennas, a transmitter, a receiver, a transceiver and/orsupporting hardware, including, for example, a processor for enablingcommunications. Via the communication interface, the example apparatusmay communicate with various other network elements in adevice-to-device fashion and/or via indirect communications.

The communications interface 858 may be configured to provide forcommunications in accordance with any of a number of wired or wirelesscommunication standards. The communications interface may be configuredto support communications in multiple antenna environments, such asmultiple input multiple output (MI MO) environments. Further, thecommunications interface may be configured to support orthogonalfrequency division multiplexed (OFDM) signalling. In some exampleembodiments, the communications interface may be configured tocommunicate in accordance with various techniques including, asexplained above, any of a number of second generation (2G), thirdgeneration (3G), fourth generation (4G) or higher generation mobilecommunication technologies, radio frequency (RF), or any of a number ofdifferent wireless networking techniques. The communications interfacemay also be configured to support communications at the network layer,possibly via Internet Protocol (IP). The user interface 860 may be incommunication with the processor 852 to receive user input from a user862 via the user interface and/or to present output to a user as, forexample, audible, visual, mechanical or other output indications. Theuser interface may include, for example, a keyboard, a mouse, ajoystick, a display (for example, a touch screen display), a microphone,a speaker, or other input/output mechanisms. Further, the processor maycomprise, or be in communication with, user interface circuitryconfigured to control at least some functions of one or more elements ofthe user interface. The processor and/or user interface circuitry may beconfigured to control one or more functions of one or more elements ofthe user interface through computer program instructions (for example,software and/or firmware) stored on a memory accessible to the processor(for example, the memory device 854). In some example embodiments, theuser interface circuitry is configured to facilitate user control of atleast some functions of the apparatus 850 through the use of a displayand configured to respond to user inputs. The processor may alsocomprise, or be in communication with, display circuitry configured todisplay at least a portion of a user interface, the display and thedisplay circuitry configured to facilitate user control of at least somefunctions of the apparatus.

In some cases, the apparatus 850 may be implemented in a chip or chipset. In an example embodiment, the chip or chip set may be programmed toperform one or more operations of one or more methods as describedherein and may include, for instance, one or more processors 852, memorydevices 854, I/O interfaces 856 and/or other circuitry componentsincorporated in one or more physical packages (for example, chips). Byway of example, a physical package may include an arrangement of one ormore materials, components, and/or wires on a structural assembly (forexample, a baseboard) to provide one or more characteristics such asphysical strength, conservation of size, and/or limitation of electricalinteraction. It is contemplated that in certain embodiments the chip orchip set can be implemented in a single chip. It is further contemplatedthat in certain embodiments the chip or chip set can be implemented as asingle “system on a chip.” It is further contemplated that in certainembodiments a separate ASIC may not be used, for example, and that allrelevant operations as disclosed herein may be performed by a processoror processors. A chip or chip set, or a portion thereof, may constitutea means for performing one or more operations of one or more methods asdescribed herein.

In general, the various examples shown may be implemented in hardware orin special purpose circuits, software, logic or any combination thereof.Some aspects may be implemented in hardware, while other aspects may beimplemented in firmware or software which may be executed by acontroller, microprocessor or other computing device, although theinvention is not limited thereto. While various aspects may beillustrated and described as block diagrams, flow charts, or using someother pictorial representation, it is well understood that these blocks,apparatus, systems, techniques or methods described herein may beimplemented in, as non-limiting examples, hardware, software, firmware,special purpose circuits or logic, general purpose hardware orcontroller or other computing devices, or some combination thereof.

Some embodiments may be implemented by computer software executable by adata processor of the mobile device, such as in the processor entity, orby hardware, or by a combination of software and hardware. Computersoftware or program, also called program product, including softwareroutines, applets and/or macros, may be stored in any apparatus-readabledata storage medium and they comprise program instructions to performparticular tasks. A computer program product may comprise one or morecomputer-executable components which, when the program is run, areconfigured to carry out methods are described in the present disclosure.The one or more computer-executable components may be at least onesoftware code or portions of it.

Further in this regard it should be noted that any blocks of the logicflow as in the Figures may represent program steps, or interconnectedlogic circuits, blocks and functions, or a combination of program stepsand logic circuits, blocks and functions. The software may be stored onsuch physical media as memory chips, or memory blocks implemented withinthe processor, magnetic media such as hard disk or floppy disks, andoptical media such as for example DVD and the data variants thereof, CD.The physical media is a non-transitory media.

The memory may be of any type suitable to the local technicalenvironment and may be implemented using any suitable data storagetechnology, such as semiconductor based memory devices, magnetic memorydevices and systems, optical memory devices and systems, fixed memoryand removable memory. The data processors may be of any type suitable tothe local technical environment, and may comprise one or more of generalpurpose computers, special purpose computers, microprocessors, digitalsignal processors (DSPs), application specific integrated circuits(ASIC), FPGA, gate level circuits and processors based on multi coreprocessor architecture, as non-limiting examples.

Examples of the disclosed embodiments may be practiced in variouscomponents such as integrated circuit modules. The design of integratedcircuits is by and large a highly automated process. Complex andpowerful software tools are available for converting a logic leveldesign into a semiconductor circuit design ready to be etched and formedon a semiconductor substrate.

The examples described herein are to be understood as illustrativeexamples of embodiments of the invention. Further embodiments andexamples are envisaged. Any feature described in relation to any oneexample or embodiment may be used alone or in combination with otherfeatures. In addition, any feature described in relation to any oneexample or embodiment may also be used in combination with one or morefeatures of any other of the examples or embodiments, or any combinationof any other of the examples or embodiments. Furthermore, equivalentsand modifications not described herein may also be employed within thescope of the invention, which is defined in the claims.

1. An apparatus, comprising: at least one processor; and at least onememory including computer program code; the at least one memory and thecomputer program code configured to, with the at least one processor,cause the apparatus to perform: transmitting a service request message;starting a service request timer when the service request message istransmitted; determining an expiration of the service request timer; andhandling the expiration of the service request timer based on a servicetype of the service request message and based on a mobility managementmode.
 2. The apparatus as claimed in claim 1, wherein the at least onememory and the computer program code are further configured to, with theat least one processor, cause the apparatus to perform: when the servicetype of the service request message is an emergency service fallbacktype, initiating at least one emergency service access; and when theservice type of the service request message is other than the emergencyservice fallback type, handling the expiration of the service requesttimer otherwise.
 3. The apparatus as claimed in claim 1, wherein the atleast one memory and the computer program code are further configuredto, with the at least one processor, cause the apparatus to perform:determining the service type of the service request message and for,when the service type of the service request message is the emergencyservice fallback type: determining the apparatus is camping on an newradio cell connected to a 5G core network, an emergency service supportindicator for access indicates that emergency services are supported inevolved universal terrestrial radio access connected to the 5G corenetwork only, and the apparatus is capable of accessing the 5G corenetwork via the evolved universal terrestrial radio access; attemptingto select an evolved universal terrestrial radio access cell connectedto the 5G core network based on the determining; and when the apparatusis unable to select an evolved universal terrestrial radio access cellconnected to the 5G core network, attempting to select an evolveduniversal terrestrial radio access cell connected to an evolved packetcore when the apparatus is configured to support S1 mode.
 4. Theapparatus as claimed in claim 1, wherein the at least one memory and thecomputer program code are further configured to, with the at least oneprocessor, cause the apparatus to perform: determining the service typeof the service request message and for, when the service type of theservice request message is the emergency service fallback type:determining the apparatus is camping on an evolved universal terrestrialradio access cell connected to a 5G core network, an emergency servicesupport indicator for access indicates that emergency services aresupported in new radio connected to the 5G core network only, and theapparatus is capable of accessing the 5G core network via a new radio;attempting to select a new radio cell connected to the 5G core networkbased on the determining; and when the apparatus is unable to select anew radio cell connected to the 5G core network, attempting to select anevolved universal terrestrial radio access cell connected to an evolvedpacket core when the apparatus is configured to support S1 mode.
 5. Theapparatus as claimed in claim 1, wherein the at least one memory and thecomputer program code are further configured to, with the at least oneprocessor, cause the apparatus to perform: determining the service typeof the service request message, and for, when the service type is theemergency service fallback type: attempting to select one of: a newradio cell connected to a 5G core network; an evolved universalterrestrial radio access cell connected to the 5G core network; andevolved universal terrestrial radio access cell connected to an evolvedpacket node further based on at least one of: an emergency servicesupport indicator for 3GPP access; a radio access technology of theapparatus' current cell; a capability to access the 5G core network viaevolved universal terrestrial radio access; support for S1 mode;availability of a suitable new radio cell connected to the 5G corenetwork, evolved universal terrestrial radio access cell connected tothe 5G core network, or evolved universal terrestrial radio access cellconnected to an evolved packet core; and an emergency service fallbackindicator for 3GPP access.
 6. The apparatus as claimed in claim 3,wherein the at least one memory and the computer program code arefurther configured to, with the at least one processor, cause theapparatus to perform: performing 5G mobility management specificprocedures and 5G service management procedures to make an emergencypacket data unit session based on determining a suitable selection ofthe new radio cell connected to the 5G core network or the evolveduniversal terrestrial radio access cell connected to the 5G corenetwork; or performing evolved packet system mobility managementspecific procedures and evolved packet system service managementprocedures to make a packet data network connection for emergency bearerservices based on determining a suitable selection of the evolveduniversal terrestrial radio access cell connected to the evolved packetcore.
 7. The apparatus as claimed in claim 1, wherein the at least onememory and the computer program code are further configured to, with theat least one processor, cause the apparatus to perform: determining theservice type of the service request message and the mobility managementmode and for, when the service type of the service request message isother than an emergency service fallback type and the mobilitymanagement mode is an idle mobility management mode: aborting theservice request procedure; releasing locally any allocated resources;selectively incrementing a service request attempt counter, wherein theservice request attempt counter is not incremented when the servicerequest procedure is configured to establish a packet data unit sessionfor emergency services, or the apparatus has an established packet dataunit session for emergency services, or the apparatus is configured forhigh priority access, or the service request was in response to a pagingor notification from a network; and based on the service request attemptcounter being equal or greater a determined threshold value performing:starting a further timer, wherein the apparatus is configured not toattempt a further service request until an expiration of the furthertimer unless at least one of: the further service request is in responseto a paging or notification from a network; the apparatus is configuredfor high priority access; the further service request is configured toestablish a packet data unit session for emergency services; theapparatus has an established packet data unit session for emergencyservices; the apparatus is registered in a new public land mobilenetwork; and when the service request was for a management objectmultimedia telephony voice call, providing to at least one upper layer anotification that the service request was not accepted.
 8. The apparatusas claimed in claim 7, wherein the at least one memory and the computerprogram code are further configured to, with the at least one processor,cause the apparatus to perform: determining the service type of theservice request message and the mobility management mode, and for, whenthe service type of the service request message is other than anemergency service fallback type and the mobility management mode is aconnected mobility management mode: aborting the service requestprocedure; and staying in the connected mobility management mode.
 9. Theapparatus as claimed in claim 1, the at least one memory and thecomputer program code are further configured to, with the at least oneprocessor, cause the apparatus to perform: initiating the servicerequest timer with a defined length value, wherein the defined lengthvalue is based on the service type of the service request message.
 10. Amethod, comprising: transmitting a service request message; starting aservice request timer when the service request message is transmitted;determining an expiration of the service request timer; and handling theexpiration of the service request timer based on a service type of theservice request message and based on a mobility management mode.
 11. Themethod as claimed in claim 10, wherein the handling the expiration ofthe service request timer based on the service type of the servicerequest message further comprises: when the service type of the servicerequest message is an emergency service fallback type, initiating atleast one emergency service access; and when the service type of theservice request message is other than the emergency service fallbacktype, handing the expiration of the service request timer otherwise. 12.The method as claimed in claim 10, wherein the handling the expirationof the service request timer based the service type of the servicerequest message further comprises: determining the service type of theservice request message and, when the service type of the servicerequest message is the emergency service fallback type: determining theapparatus is camping on an new radio cell connected to a 5G corenetwork, an emergency service support indicator for access indicatesthat emergency services are supported in evolved universal terrestrialradio access connected to the 5G core network only and the apparatus iscapable of accessing the 5G core network via the evolved universalterrestrial radio access; attempting to select an evolved universalterrestrial radio access cell connected to the 5G core network based onthe determining; and when the apparatus is unable to select an evolveduniversal terrestrial radio access cell connected to the 5G corenetwork, attempting to select an evolved universal terrestrial radioaccess cell connected to an evolved packet core when the apparatus isconfigured to support S1 mode.
 13. The method as claimed in claim 10,wherein the handling the expiration of the service request timer basedon a service type of the service request message further comprises:determining the service type of the service request message and, whenthe service type of the service request message is the emergency servicefallback type: determining the apparatus is camping on an evolveduniversal terrestrial radio access cell connected to a 5G core network,an emergency service support indicator for access indicates thatemergency services are supported in new radio connected to the 5G corenetwork only, and the apparatus is capable of accessing the 5G corenetwork via a new radio; attempting to select a new radio cell connectedto the 5G core network based on the determining; and when the apparatusis unable to select a new radio cell connected to the 5G core network,attempting to select an evolved universal terrestrial radio access cellconnected to an evolved packet core when the apparatus is configured tosupport S1 mode.
 14. The method of claim 10, wherein the handling theexpiration of the service request timer based on the service type of theservice request message and the mobility management mode furthercomprises: determining the service type of the service request messageand the mobility management mode and, when the service type of theservice request message is other than an emergency service fallback typeand the mobility management mode is an idle mobility management mode:aborting the service request procedure; releasing locally any allocatedresources; selectively incrementing a service request attempt counter,wherein the service request attempt counter is not incremented when theservice request procedure is configured to establish a packet data unitsession for emergency services, or the apparatus has an establishedpacket data unit session for emergency services, or the apparatus isconfigured for high priority access, or the service request was inresponse to a paging or notification from a network; and based on theservice request attempt counter being equal or greater a determinedthreshold value performing: starting a further timer, wherein theapparatus is configured not to attempt a further service request untilan expiration of the further timer unless at least one of: the furtherservice request is in response to a paging or notification from anetwork; the apparatus is configured for high priority access; thefurther service request is configured to establish a packet data unitsession for emergency services; the apparatus has an established packetdata unit session for emergency services; the apparatus is registered ina new public land mobile network; and when the service request was for amanagement object multimedia telephony voice call, providing to at leastone upper layer a notification that the service request was notaccepted.
 15. A computer program embodied on a non-transitorycomputer-readable medium, said computer program comprising program codeconfigured to perform the method according to claim 10, when thecomputer program product is executed on a computer.